I don't know if many of you guys realize, but this whole pledging-money-to-get-motivated business is a very upper-middle-class thing to do. The decision to motivate yourself in this way looks very different depending on whether there still are plenty of ways to spend your money on an assured and tangible improvement to your life. Simply put, one's willingness to engage in this sort of contract signals that you have the money needed to not really feel the loss, and a general lack of awareness of how much it sucks to actually feel the loss. (If you think that you wouldn't mind the possibility of things really sucking as long as the fear of it motivates you to put in some extra effort, there's somebody for whom things actually suck that would really like more money and less pressure. OP may really be happy to switch places with the guy in Fight Club, but I'd bet your ass the guy in Fight Club would also want to switch places with him.)

If you're on the poorer side of the income spectrum, chances are there's some costly stuff that comes higher in your priority list than motivating yourself with money, and usually it's economically rational to go for them instead. Example: until recently I didn't really have a proper desk at which I could write. My desk was really tiny and my desktop computer took up basically all the space on it, so if I wanted to, say, do some exercises from my math workbook I wouldn't have space to spread out all my stuff, and would have to place the exercise book on my knees, or go write on the bed and sit all cramped and frequently have to change position because of back pain (or knee, or elbow). The physical discomfort had a contribution in putting me off studying, and I wasn't too eager in the first place. The proper thing to do with my money back then, if I wanted to improve my likelihood of studying, was not to motivate myself with fear of loss, but to save up for a new damn desk (and a chair that wasn't 12 years old and hard as concrete).

And, of course, it's completely inapplicable to goals related to making or saving money; that would be just like kicking yourself in the foot.

The reason I'm saying this is that this place kind of feels like upper-middle-class people talking to other upper-middle-class people, not realizing that their way of spending money is the upper-middle-class way rather than the universally economically rational way. If it works in your case, then good for you, but there are poorer people in this world, we're here, we exist, and it would be kind of nice to take into consideration the fact that some motivational strategies are not a good idea for everyone. (And if you say they should work all the more so the poorer you are, because then you'll have more to lose -- well, I don't want to say "check your privilege", but... check your privilege.)

BTW, an important question to answer about this system would be "who does the money go to, and why, and are they aware of it?". Because, if there's a common economic agent to which people who do this tend to give their money to -- say, a charity who gets wise of this tendency, or a person who has a lot of friends who do this -- they'd have this really sweet incentive to try and get you to fail.